I18N of the extension itself
Should be pretty easy to implement, but I don't know yet how to get people to help with translating the strings.
Relevant docs: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Internationalization
There's always some volunteers who like to help out doing this, at least for Indian languages.
Mozilla has some sort of portal to make it easier for people to contribute translations. I wonder if there is a public version of this where we can have people contribute strings without having to do GitHub, or edit JSON files manually
https://alternativeto.net/software/weblate/